Negative transconductance tubeoscillator



foct. 15, 1940. E, w HEROLD 2,217,748

NEGATIVE TRANSCONDUCTANCE TUBE-OSCILLATOR @Filed Nov. 26, 19:5'

m d I 5 ourPur cmcu/rw ,l 9

|m F Ht;

ourkur emu/r.

OUTPUT CIRCUIT INVENTOR EDWA RD W. EROLD I ATTORNEY Patented Oct. 15,1940 NEGATIVE TRAN SC'ONDUCT'ANGE TUBE- OSCILLATOR Edward W. Herold,Verona, N. J., assignor to Radio Corporation of America, a corporationof Delaware Application November 26, 1937. Serial No. 176,548

8 Claims.

This invention relates to electron tube circuit arrangements suitablefor use particularly as oscillators or as amplifiers. It is a feature ofthe circuits herein shown that they provide for the operation of anelectron tube under conditions in which the tube characteristicexhibitsa. negative transconductance. By transconductance is meant the ratio ofthe change in the current in the circuit of an electrode to the changein the voltage of another electrode under the condition that all othervoltages remain unchanged. A negative transconductance, therefore, wouldbe exhibited where the output current falls while increasing the voltageon the control electrode, or where the control voltage is made lessnegative with respect to the potential of the cathode.

It is an object of my invention to provide suitable elements incombination and to assign suitable values to the various component partsof an electron tube circuit so that a negative transconductancecharacteristic may be exhibited.

It is a further object of my invention to provide a circuit arrangementwhere a retarding field type of negative transconductance tube having anauxiliary anode may be employed, the function of this auxiliaryanodebeing to collect the electrons which are permitted to pass through thecontrol grid.

As is commonly known, tubes of the type above mentioned may be used forthe production of sinusoidal or relaxation oscillations in simplecircuits. If any attempt is made to utilize these oscillations byconventional methods of coupling to the oscillating circuit, it is foundthat variations in the loading are accompanied by variations in theoscillator frequency, and amplitude, an efi'ect obviously undesirable.

In order to reduce this objectionable characteristics it was heretoforethought necessary to insert an intermediate stage of amplificationbetween the oscillator and the load circuit. Accordingly, it is afurther object of my invention to devise a circuit arrangement which issimpler than those heretofore used in that the requirement for anintermediate amplifier ,stage is eliminated. I have found that thisadvantageous result can be obtained by the employment of a. retardingfield type tube having an auxiliary anode as the output electrode,the-load circuit being connected to or coupled to this auxiliary anode.Since variations in the auxiliary anode potential have little effect onthe negative transconductance portion of the tube which is in the screenretarding field of such a tube, it .isapparent that variations in theloading of this anode circuit are practically ineffective in producingchanges in the oscillating portionof the same tube.

My invention will be explained in more detail by reference to theaccompanying drawing, in which I Figure 1 shows a preferred circuitarrangement having a special type of electron discharge tube theelectrodes of which are'connected in a suitable manner and have suitablepotentials applied thereto for obtaining the advantageous oscillatingcharacteristics set forth in the foregoing objects of the invention; IFig. 2 shows a modified circuit arrangement in which apiezo-electriccrystal may be added Fig. 3 shows still another modification in which apiezo-electric crystal is also used but with the connections theretomade in a different manner than as shown in Fig. 2, and Fig. 4represents still another modification in which a piezo-electric crystalis preferably connected between one anode and the cathode.

Referring first to Fig. 1, this. circuit shows diagrammatically aspecial type of electron discharge tube 5, this tube being one: whichexhibits a negative transconductance characteristic when connected inthe manner shown and described. In the instant application I am makingno claim to the features of novelty of the tube itself, since thatnovelty which it possesses is being claimed in my Patent No. 2,139,366granted December 6, 1938. A tube having negative transconductanceappears to have beenused in the past in what is known as a VanderPolrelaxation oscillator circuit. (See Philosophical Magazine, volume 2,pages 978, 992, 1926.) A feature of the tube shown in this applicationis that it includes a cathode 6, two grids 1 and 8 respectively, and twoanodes 9 and iii respectively.

VanderPol attributed the oscillations to a relaxation process, whichinherently produces highly distorted wave forms. At a later period, andunaware of the relation of the earlier work to my'own, I investigatedthe nature of oscillations in a somewhat different circuit, using anegative transconductance tube. I discovered that oscillationsessentially true to the sine-wave form could be produced when theamplitudes were held relatively small. When the prior work of VanderPolcame to my attention, I found that my discovery. of this important facthad not previously been observed. My own analysis set forth in detailthe theory of the sinusoidal oscillations and derived the conditions foroscillation and forthe control of frequency. ,(See my PATENT ori cepaper published in Proceedings of I. R. E., volume 23, pages 1201-1223,October 1935.)

I will first describe certain typical circuit arrangements whichillustrate the features of the invention, after which the operatingcharacteristics will be discussed.

According to the embodiment shown in Fig. 1, the tube 5 is provided withan input circuit extending from the grid 1 through a grid leak resistorl3 and biasing battery IE to the cathode 6. The output circuit extendsfrom the anode l0 through any utilization device and through anodepotential source 4 and screen grid potential source 3 to the cathode 6.An auxiliary imperforate anode 9 is disposed adjacent the cathode 6 andis coupled to the input circuit by means of a capacitor II. A suitableanode potential is supplied to this anode 9 from the source 4 by meansof a circuit which includes a resistor I4.

The circuit arrangement of Fig. 2 is similar to that of Fig. 1 exceptthat in place of the coupling capacitor II I preferably employ a piezoelectric device l2.

The'circuit arrangement of Fig. 3 difiers from that shown in Fig. 2principally in respect to the disposition of the piezo electric device.In this case it is disposed in shunt with the resistor l3 and issupplementary to the capacitor H which is retained in accordance withthe arrangement shown in Fig. 1.

In the embodiment shown in Fig. 4 I preferably dispose the p-iezoelectric device in shunt with the resistor l4 and also retain the use ofthe coupling capacitor ll between the auxiliary anode 9 and the grid 1.

When the circucit arrangement of Fig. 1 is chosen, oscillations areproduced in that portion of the tube 5 which includes the cathode 6, thecontrol grid 1 and the anode 9. The circuit arrangement is such thatenergy is fed back across a capacitor ll between the control grid 1 andthe anode 9. The output circuit is connected from the cathode 6 throughthe screen. grid source 3 and auxiliary anode potential source 4 throughany suitable load to the auxiliary anode ID. This circuit is shieldedfrom the oscillator circuit by means of the screen grid 8. In fixing thevalues to be assigned to portions of the circuit externally of the tube5, certain internal capacitances must be taken into consideration. Forexample, there is the capacitance Cg between the grid 1 and the anode 9.There is also an inter-electrode capacitance Cp between the anode 9 andthe cathode 6.

In order to stabilize the frequency of such an oscillator apiezo-electric device 12 may be employed in place of the capacitor II.This modification is shown in Fig. 2. The circuit arrangement shown inFig. 2 includes a resistor l3 connected between the grid 1 and thebiasing source I5, the positive side of the latter being connected tothe cathode 6. Another resistor I4 is connected from the positive sideof the source It to the anode 9. By a correct choice of resistive valuesfor the elements [3 and Hi the fundamental oscillating frequency of thecircuit in the absence of the crystal may be determined. Uponintroducing thecrystal, however, the efiective shunt capacitance of thecrystal holder between the control grid and the anode 9 must be takeninto consideration with due regard to the crystal frequency. Theintroduction of the crystal will maintain oscillationsat the naturalfrequency of the crystal, the frequency remaining essentially a and thebiasing source 15.

stable as in the more conventional quartz stabilized oscillatorcircuits.

The circuit arrangement shown in Fig. 2 may be employed to produceoutput frequencies which are multiples or submultiples of the crystalfrequency. As a frequency multiplier or divider the circuit possessesthe advantages of simplicity and stability.

Referring now to Fig. 3, I show a modification in which in addition tothe capacitor l I connected as shown in Fig. 1 I also employ apiezo-electric crystal l2 connected between the control grid Thepiezo-electric crystal and the resistor l-3 are, therefore,shuntconnected. In certain cases the inherent tube capacitance may be.sufficient so that the use of the capacitor ll externally to the tubebecomes unnecessary.

Referring to the embodiment shown in Fig. 4, I show how thepiezo-electric crystal I2 may be inserted in shunt with the resistor 14.The other elements of the circuit combination are substantially the sameas shown in Fig. 3. This circuit arrangement has advantageous featuresunder certain operating conditions and the choice between the employmentof either of the circuits of Figs. 3 and 4 is left largely to thediscretion of the user.

Other modifications of my invention will be suggested by the foregoingspecification. It will be found that in particular applications theaddition of tuned circuits across any of the three major portions of thecircuit arrangement, while contributing to the advantageous results tobe sought, are not to be considered essential. It is a conspicuousfeature of the circuit arrangements shown that stability of oscillationgeneration is obtained without recourse to tuned circuits.

In the foregoing disclosure of my invention only one type ofnegative-transconductance tube has been shown and described. It shouldbe understood, however, that the circuits shown are directly applicableto other forms of negative transconductance tube, and that any specifictype of tube in that generic class may be adopted in the circuits of myinvention without departing from the spirit thereof.

While various uses of my improved negative transconductance tube circuithave been suggestr ed in the foregoing, it may be worthy of note thatother uses are contemplated such as shown, for example, in my copendingapplication, Serial No. 148,461, filed June 16, 1937. In this lastmentioned application methods are described wherein the negativetransconductance tube may be used as an amplifier. In the instantapplication, however, I am laying stress upon the use of such a tube asan oscillator, or frequency changer.

The claims to follow are to be given the broadest interpretation whichthe language thereof will permit.

I claim:

1. A system for obtaining energy feed-back in a negativetransconductance oscillator tube, said tube having a cathode, aplurality of grids, an output anode and an auxiliary imperforate anode,means for diverting a portion of the electrons flowing toward the outputanode, means for causing said electrons to be collected by saidauxiliary anode, thereby producing an oscillation generating controlpotential, means for impressing said control potential upon the controlgrid of said tube, and means including a piezo electric device forstabilizing the frequency of the control grid circuit.

2. In combination with an electron discharge tube having a cathode, aplurality-of grids, an output anode and an auxiliary imperforate anode,means for mounting said anodes so that a portion of the electron streamflowing toward the output anode may be diverted and collected by theother anode, circuit means connecting said grids to said cathode, asource of operating potentials suitably applied to said electrodes, aload element connected between the cathode and the output anode, and apiezo electric device connected between the auxially anode and one otherelectrode of said tube, said auxiliary anode having a capacitivelycoupled feedback connection to one of said grids, whereby substantiallysinusoidal oscillations are generated.

3. In combination with a discharge tube having at least a cathode, acontrol grid, an output anode and an auxiliary imperforate electrodepositioned to receive an increased number of electrons when the controlgrid is rendered more negative, an input circuit connected between thecathode and control grid, an output circuit including a source ofoperating potentials and a load connected between said cathode and saidoutput anode, a circuit from said source of operating potentials to theauxiliary electrode, and means capacitively coupling said auxiliaryelectrode to said control grid whereby substantially sinusoidaloscillations are generated independently of load variations.

4. The combination set forth in claim 3 and having means including apiezo-electric device connected between two of the electrodes in saidtube, for fixing the frequency of the oscillations generated.

5. An oscillator circuit arrangement comprising an electron dischargetube having a cathode, a control grid, a screen grid, an output anodeand an auxiliary anode, the two said anodes being imperforate, and theoutput anode being shielded by said screen grid from the remainingelectrodes, a substantially purely resistive and non-inductive inputcircuit, including a grid biasing source, connected between the cathodeand control grid, feed-back coupling means connected between saidauxiliary anode and said control grid, a piezoelectric device in circuitbetween two of the electrodes in said tube, an output circuit includinga source of operating potentials and a load, said output circuit beingconnected between the oathode and said output anode, a substantiallypurely resistive and none-inductive circuit from said source ofoperating potentials to said auxiliary anode, a connection from saidsource to said screen grid, and means for so fixing the values of theworking potentials applied to said electrodes in relation to theircapacitances that said tube is caused to exhibit a negativetransconductance characteristic.

6. A circuit arrangement in accordance with claim 5 and having saidpiezo-electric device connected between said control electrode and saidcathode. 1

7. A circuit arrangement in accordance with claim 5 and having saidpiezo-electric device connected between said control electrode and saidauxiliary anode.

8. A circuit arrangement in accordance with claim 5 and having saidpiezo-electric device connected in circuit between said anode and saidcathode auxiliary.

EDWARD W. HEROLD.

